The inventive concept relates generally to sensors and methods of operating sensors. More particularly, the inventive concept relates to depth information calculations, depth sensors that use a time of flight (TOF) principle, image capture methods using a depth sensor, and image processing systems including a depth sensor.
A “sensor” is a device that detects the state of an object and transforms a detection result into a corresponding electrical signal. Certain sensors are also capable of communicating the corresponding electrical signal to a variety of external circuits.
Sensors include light sensors, temperature sensors, pressure sensors, magnetic sensors, and so-called depth (or distance) sensors. The term “depth sensor” is used to denote a class of sensors that detects—as one type of state—the location (or relative location) of the object. Sensors may be used to detect the state of an object in relation to a particular range of electromagnetic signals, such as microwave signals, visible light signals, infrared signals, ultrasonic signals, etc. In certain applications, a sensor will be associated with a “source” that transmits (or emits) a “source signal” or ranging signal towards an object. The object may then reflect a portion of the source signal, and the reflected portion of the source signal is detected by a depth sensor.
In this manner, a depth sensor may measure a depth (or range. or distance) between the object and the sensor using a TOF measuring method. That is, the depth sensor may be used to measures a delay time between the transmission (or emission) of the source signal and return of the reflected portion of the source signal to the sensor. In this context, an area surrounding the object, an area effectively receiving transmission of the source signal, and/or an area effectively detected by the sensor may be termed a “scene”.
When a depth sensor is disposed relatively far from a scene, the level of the source signal reaching the scene and/or the level of the reflected portion of the source signal returned to the depth sensor may be relatively low. A low source signal level adversely affects the signal-to-noise ratio for the reflected portion of the source signal. That is, the depth sensor will received a relatively large quantity of noise along with the relatively weak reflected portion of the source signal.
In contrast, when the depth sensor is relatively close to a scene, the level of the reflected portion of the source signal will be relatively high, thereby providing a good signal-to-noise ratio. Unfortunately, many scenes contain some objects that are far from the depth sensor and other objects that are near the depth sensor. And it is often difficult to capture images from a complex assortment of signals reflected from both near and far objects or scene portions. Accordingly, there is a demand for methods that increase the overall accuracy of depth information provided by depth sensors, particularly as such depth information relates to scenes having multiple objects separated near and far from the depth sensor.